Full_Name: Peter Mogensen Version: 2.4.20 OS: any URL: ftp://ftp.openldap.org/incoming/ Submission from: (NULL) (95.166.36.16)
All of the examples about mirrormode in the admin guide tells you to set ServerID to "1" and "2". The extended form (ServerID <N> <URL>) is only mentioned for N-way multimaster.
However, IF you also setup mirrormode for cn=config, you need to specify ServerID on both servers as:
ServerID 1 ldap://server1/ ServerID 2 ldap://server2/
... so the config is the same on both server. Else your replica will not receive all updates and servers will think changes they made them self are made by others.
A user might be able to figure this out be thinking about what mirroring cn=config actually requires, but it would probably some time if this is mentioned in section 18.3.4 of the admin guide.